This invention relates to a non-contact type dimensional gage and particularly to one for measuring the curvature of workpieces such as turned parts.
In producing precision turned workpieces, it is frequently necessary to carefully control workpiece diameters. Diameter values provide direct information about the quality of the part, the state of the machining process, and the cutting tool condition and positioning. In one general category of gaging apparatuses, finished workpieces are applied to gaging blocks or dimensional checking fixtures for measurement. Various types of such gaging systems are known, including those using dial indicators, touch probes, caliper gages, air gages, triangulation gages, laser scanning gages, etc. Such devices may be used in closed loop machining processes in which information about workpiece dimensions is used to adjust tool position, thus compensating for tool wear, etc. While such "post-process" gages are well adapted for numerous uses, there is a need to provide a gage which also can be used for "in-process" measurement which permits continual monitoring of workpiece diameter during the machining process. With this type of gaging, closed loop control for the machining operation for each workpiece can be provided, thus correcting for workpiece dimensional deviations. There is also a need to provide a non-contact type gage which does not rely on physical contact between two parts which gives rise to gage and workpiece wear. It is a further desirable feature for such a device to provide machining tool clearance without interfering with the gaging process. As a means of providing enhanced accuracy, it is advantageous for the gage to provide self-contained measurement which does not depend upon a remotely located datum, since the mechanisms coupling the gage to the datum can give rise to measurement errors.